Brain Pathology Case of the Month - January 2013

A 40-year-old male with a one year clinical history of vertigo and intermittent headaches was admitted for evaluation at a tertiary university hospital. Magnetic Resonance Image (MRI) showed a heterogenously enhancing mass with cystic and calcific components in the anterior horn of the left lateral ventricle measuring 2.5 x 2.2 x 1.6 cm (Fig. 1). The patient underwent partial resection of the intraventricular tumor through a left frontal craniotomy with transfrontal approach to the left ventricle. The patient was discharged four days later and has done well since that time with no neurological deficits.

PATHOLOGICAL FINDINGS

The H&E sections showed a neoplasm which in most areas was composed of elongated spindle cells arranged in a fascicular pattern (Fig. 2). Some areas were more cellular and showed mild nuclear pleomorphism, while others were hypocellular and composed mainly of fibrillary cell processes. Some of the hypocellular areas showed clustered nuclei surrounded by a fibrillary stroma and merged into foci with a microcystic appearance (Fig. 3). In addition there were rare collections of large pleomorphic glial cells with a ganglionic appearance (Fig. 4). The Ki-67 immunostain showed a low proliferative index. The tumor cells were strongly immunoreactive for glial fibrillary acidic protein (GFAP) (Fig. 5) and S-100 protein (Fig. 6), but showed no immunoreactivity for epithelial membrane antigen (EMA). The synaptophysin immunostain showed focal entrapment of pre-existing axons, but there was not too much diffuse infiltration of pre-existing parenchyma. Electron microscopy was helpful (Fig. 7). What is the diagnosis?